The Collaborative International Dictionary of English v.0.48:

Arch \Arch\, n. [See Arch-, pref.]
   A chief. [Obs.]
   [1913 Webster]

         My worthy arch and patron comes to-night. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

-arch \-arch\ [Gr. 'archo`s chief, commander, 'a`rchein to rule.
   See Arch, a.]
   A suffix meaning a ruler, as in monarch (a sole ruler).
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arch \Arch\, v. t. [imp. & p. p. Arched ([aum]rcht); p. pr. &
   vb. n. Arching.]
   1. To cover with an arch or arches.
      [1913 Webster]

   2. To form or bend into the shape of an arch.
      [1913 Webster]

            The horse arched his neck.            --Charlesworth.
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The Collaborative International Dictionary of English v.0.48:

Arch \Arch\, v. i.
   To form into an arch; to curve.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arch \Arch\ ([aum]rch), n. [F. arche, fr. LL. arca, for arcus.
   See Arc.]
   1. (Geom.) Any part of a curved line.
      [1913 Webster]

   2. (Arch.)
      (a) Usually a curved member made up of separate
          wedge-shaped solids, with the joints between them
          disposed in the direction of the radii of the curve;
          used to support the wall or other weight above an
          opening. In this sense arches are segmental, round (i.
          e., semicircular), or pointed.
      (b) A flat arch is a member constructed of stones cut into
          wedges or other shapes so as to support each other
          without rising in a curve.
          [1913 Webster]

   Note: Scientifically considered, the arch is a means of
         spanning an opening by resolving vertical pressure into
         horizontal or diagonal thrust.
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   3. Any place covered by an arch; an archway; as, to pass into
      the arch of a bridge.
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   4. Any curvature in the form of an arch; as, the arch of the
      aorta. "Colors of the showery arch." --Milton.
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   Triumphal arch, a monumental structure resembling an arched
      gateway, with one or more passages, erected to commemorate
      a triumph.
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The Collaborative International Dictionary of English v.0.48:

Arch- \Arch-\ ([aum]rch-, except in archangel and one or two
   other words). [L. arch-, Gr. 'arch- = 'archi-. See Arch-.]
   A prefix signifying chief, as in archbuilder, archfiend.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Arch \Arch\ ([aum]rch), a. [See Arch-, pref.]
   1. Chief; eminent; greatest; principal.
      [1913 Webster]

            The most arch act of piteous massacre. --Shak.
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   2. Cunning or sly; sportively mischievous; roguish; as, an
      arch look, word, lad.
      [1913 Webster]

            [He] spoke his request with so arch a leer.
                                                  --Tatler.
      [1913 Webster]

WordNet (r) 3.0 (2006):

arch
    adj 1: (used of behavior or attitude) characteristic of those
           who treat others with condescension [syn: arch,
           condescending, patronizing, patronising]
    2: expert in skulduggery; "an arch criminal"
    3: naughtily or annoyingly playful; "teasing and worrying with
       impish laughter"; "a wicked prank" [syn: arch, impish,
       implike, mischievous, pixilated, prankish, puckish,
       wicked]
    n 1: a curved shape in the vertical plane that spans an opening
    2: a curved bony structure supporting or enclosing organs
       (especially the inner sides of the feet)
    3: a passageway under a curved masonry construction; "they built
       a triumphal arch to memorialize their victory" [syn: arch,
       archway]
    4: (architecture) a masonry construction (usually curved) for
       spanning an opening and supporting the weight above it
    v 1: form an arch or curve; "her back arches"; "her hips curve
         nicely" [syn: arch, curve, arc]

Moby Thesaurus II by Grady Ward, 1.0:

280 Moby Thesaurus words for "arch":
   Machiavellian, Machiavellic, acute, apse, arc, arcade, arcature,
   arch over, arched roof, archway, artful, astute, banner, bantam,
   barrow, basket-handle arch, bend, bend back, bestraddle, bestride,
   bold, boundary stone, bow, brass, bridge, bust, cagey, cairn,
   camber, canny, capital, cardinal, ceilinged roof, cenotaph,
   central, champion, cheeky, chief, clever, clubfoot, cocky, column,
   concameration, concha, conspicuous, consummate, coquettish, cove,
   coy, crafty, cromlech, crook, cross, crowning, cunning, cup,
   cupola, curl, curvation, curvature, curve, cute, cyclolith,
   deceitful, decurve, deep, deep-laid, deflect, derisive, designing,
   devilish, digit, diplomatic, dog, dolmen, dome, dominant, elfish,
   elvish, embow, extend over, extraordinary, extreme, extremity,
   feline, fetlock, first, flex, flippant, focal, foolish, foot,
   footstone, forefoot, foremost, forepaw, foxy, fresh,
   full of mischief, geodesic dome, grave, gravestone, great,
   greatest, guileful, hang over, harefoot, head, headmost, headstone,
   heel, hegemonic, high-spirited, hoarstone, hoof, hook, hump, hunch,
   igloo, imbricate, impish, incurvate, incurve, inflect, ingenious,
   inscription, insidious, instep, inventive, jut, keystone, knavish,
   knowing, lap, lap over, leading, lie over, loop, magisterial, main,
   major, malapert, marker, master, mausoleum, megalith, memento,
   memorial, memorial arch, memorial column, memorial statue,
   memorial stone, menhir, mischief-loving, mischievous, mocking,
   monolith, monument, mound, necrology, notable, noteworthy, obelisk,
   obituary, ogive, overarch, overhang, overlap, overlie, override,
   overruling, pad, paramount, pastern, patte, paw, pawky,
   pedal extremity, pedes, pert, pes, pied, pillar, plaque, playful,
   politic, prankish, pranksome, pranky, predominant, preeminent,
   premier, preponderant, prevailing, primal, primary, prime,
   principal, prize, puckish, pug, pyramid, ranking, ready, recurve,
   reflect, reflex, reliquary, remembrance, resourceful, retroflex,
   ribbon, roguish, rostral column, round, ruling, sag, saucy,
   scampish, scapegrace, scheming, serpentine, shaft, sharp, shifty,
   shingle, shrewd, shrine, skewback, slick, slippery, sly, smooth,
   snaky, sneaky, sole, sophistical, sovereign, span, splayfoot,
   sportive, star, stealthy, stela, stellar, stone, strategic, stupa,
   subtile, subtle, supereminent, supple, swag, sweep, tablet,
   tactical, testimonial, toe, tomb, tombstone, tootsy, tope,
   topflight, trefoil arch, trickish, tricksy, tricky, trophy,
   trotter, turn, twitting, ungula, vault, vaulting, voussoir,
   vulpine, waggish, wary, wily, wind



Easton's 1897 Bible Dictionary:

Arch
   an architectural term found only in Ezek. 40:16, 21, 22, 26, 29.
   There is no absolute proof that the Israelites employed arches
   in their buildings. The arch was employed in the building of the
   pyramids of Egypt. The oldest existing arch is at Thebes, and
   bears the date B.C. 1350. There are also still found the remains
   of an arch, known as Robinson's Arch, of the bridge connecting
   Zion and Moriah. (See TYROPOEON VALLEY.)